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The term hypercalcemia refers to having too much calcium in the blood. For some, the cause is an overactive parathyroid gland, certain medications, too much vitamin D, or underlying health conditions, including cancer.

Calcium plays an essential role in the body. It helps to build strong bones and teeth, while also supporting the muscles, nerves, and heart. However, too much calcium can lead to problems.

In this article, we explore the symptoms, causes, and complications of hypercalcemia. We also describe how it can be diagnosed and treated.

What is hypercalcemia?

The parathyroid gland controls calcium levels in the blood.

Calcium levels in the blood are mostly controlled by the parathyroid glands. These four tiny glands sit behind the thyroid.

When the body needs calcium, the parathyroid glands secrete a hormone. This hormone signals:

the bones to release calcium into the blood

the kidneys to excrete less calcium into the urine

the kidneys to activate vitamin D, which helps the digestive tract to absorb more calcium

Overactive parathyroid glands or an underlying health condition can disrupt the balance of calcium.

If calcium levels become too high, a person may be diagnosed with hypercalcemia. This condition can impede bodily functions, and may specifically be associated with:

High blood pressure and abnormal heart rhythms. High levels of calcium can increase blood pressure and lead to electrical abnormalities that change the heart's rhythm, adding strain.

Causes

A number of factors and underlying conditions can cause hypercalcemia. These include:

Overactive parathyroid glands

The parathyroid glands control calcium levels. If they work too hard, this can lead to hypercalcemia.

The parathyroid glands may become overactive when one is enlarged or when a noncancerous growth forms on one.

Having overactive parathyroid glands is called hyperparathyroidism. This may be the most common cause of hypercalcemia.

Hyperparathyroidism is usually diagnosed in people aged between 50 and 60. It is also up to three times more common in women than men.

Too much vitamin D

Vitamin D triggers calcium absorption in the gut. Once absorbed, calcium travels into the bloodstream.

Only 10–20 percent of the calcium in the diet is usually absorbed, while the rest is passed in stools. However, excessive amounts of vitamin D cause the body to absorb more calcium, leading to hypercalcemia.

In 2012, some researchers suggested that therapeutic high-dose vitamin D supplementation has the potential to cause hypercalcemia. These supplements can be used in the treatment of multiple sclerosis and other conditions.

The Food and Nutrition Board in the United States defines high doses of vitamin D as more than 4,000 international units (IU) per day. The recommended daily dose for adults is 600–800 IU per day.

Cancer

If a person has cancer, this may cause hypercalcemia. Cancers that commonly lead to this condition include:

In 2013, it was estimated that each year hypercalcemia affects more than 2 percent of all cancer patients in the U.S. Also, up to 30 percent of people with cancer will have high levels of calcium over the course of the disease.

If cancer spreads to the bone, this increases the risk of hypercalcemia.

Reduced mobility

People who are unable to move around for long periods may also be at risk for hypercalcemia. When the bones have less work to do, they can weaken and release more calcium into the bloodstream.

Severe dehydration

People who are severely dehydrated have less water in their blood, which can increase the concentration of calcium in the bloodstream. However, this imbalance is usually corrected once a person becomes sufficiently hydrated.

In some cases, high levels of calcium can lead to severe hydration. It is important for doctors to identify which came first: the high levels of calcium or the dehydration.

Medications

Some medications can overstimulate the parathyroid gland, and this can lead to hypercalcemia. One example is lithium, which is sometimes used to treat bipolar disorder.

Complications

Without proper treatment, hypercalcemia can be associated with:

Osteoporosis

Hypercalcemia may be associated with osteoporosis

Over time, the bones may release excessive amounts of calcium into the bloodstream. This makes the bones thinner, or less dense. As calcium continues to be released, osteoporosis can develop.

Kidney stones

People with hypercalcemia are at risk of developing calcium crystals in their kidneys. These crystals can become kidney stones, which are often very painful. They can also lead to kidney damage.

Kidney failure

Over time, severe hypercalcemia can stop a person's kidneys from working correctly. The kidneys may become less effective at cleaning the blood, producing urine, and efficiently removing fluid from the body. This is called kidney failure.

Problems with the nervous system

If left untreated, severe hypercalcemia may impede the nervous system. Possible effects include:

Treatment

People with mild hypercalcemia may not require treatment, and levels may return to normal over time. The doctor will monitor calcium levels and the health of the kidneys.

If calcium levels continue to rise or do not improve on their own, further testing will likely be recommended.

For people with more severe hypercalcemia, it is important to discover the cause. The doctor may offer treatments to help lower calcium levels and prevent complications. Possible treatments include intravenous fluids and medications such as calcitonin or bisphosphonates.

If overactive parathyroid glands, too much vitamin D, or another health condition is causing hypercalcemia, the doctor will also treat these underlying conditions.

A person with a noncancerous growth on a parathyroid gland may require surgery to remove it.

Prevention

Certain lifestyle changes can help to keep calcium levels balanced and bones healthy. These include:

Drinking plenty of water. Staying hydrated may lower blood calcium levels, and it can help to prevent kidney stones.

Quitting smoking. Smoking can increase bone loss. In addition to improving the health of the bones, quitting will reduce the risk of cancer and other health problems.

Exercising and strength training. This promotes bone strength and health.

Following guidelines for medications and supplements. Doing so may decrease the risk of consuming too much vitamin D and developing hypercalcemia.

Outlook

A person's outlook depends on the cause and severity of hypercalcemia.

Mild hypercalcemia may not require treatment. If the condition is more serious, a doctor may prescribe medications that lower levels of calcium and treat the underlying cause.

Anyone experiencing symptoms of hypercalcemia should speak with a doctor.

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